As a single general for the campaign could not be agreed upon because of the fragmented and fractious nature of the nobles, Amenheraft's proposed method seemed to be the best possible solution.
This compromised command structure did not fully please any group, but at least placated most, even Faruq, who viewed his given authority as being adequate.
And as for the obvious question of 'why Maizdy could be chosen' but 'not Muazz', ignoring the mindset he was in, unqualified to even lead a village of peasants, nevermind a full army,
it was because -
One-Muazz had his chance once and chose his son as the general,
Two- he was a terrible commander,
And three, most importantly, the nobles did not want to see this man use their army to get his city back.
They wanted to be the ones to retake Zanzan, and then metaphorically slaughter the fat Pasha in exchange for it, using absurd trade deals, huge land reallotment, peerage increases, and even just a huge lump sum of money.